Variable displacement dual vane pump

ABSTRACT

The present invention is a variable displacement pump having an inner rotor rotatable about a first axis and having at least two slots. The pump also has at least two vanes, each located in a distinct one of the at least two slots. The pump also has an outer rotor rotatable about a second axis, operably associated with the inner rotor, the outer rotor having two or more recesses, each configured to receive one of the vanes. The pump also includes an expandable chamber formed by the outer rotor and the inner rotor, an eccentric ring surrounding the outer rotor, and a housing. The eccentric ring is located within the housing for adjusting the relative relationship between the first axis and the second axis in order to vary the displacement of the pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a PCT International Application of U.S. Patent Application No. 60/922,683 filed on Apr. 10, 2007. The disclosure of the above application is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to sliding vane pumps; more particularly, the present invention relates to sliding vane pumps having a stacked integrated vane configuration.

BACKGROUND OF THE INVENTION

Sliding vane pumps are commonly used to transfer fluid from an inlet port to an outlet port. Typically, they have a ring which is eccentric, and an inner rotor; the inner rotor is typically fixed to and rotates with a shaft, and a series of vanes slide in and out of a set of vane slots. As the vanes rotate with the inner rotor, the vanes will slide along the inner surface of the eccentric ring. The eccentricity between the inner rotor and the eccentric ring can be varied to vary the amount of fluid that is displaced by the pump.

Current designs for sliding vane pumps have several disadvantages, the most common of which relates to the wear that occurs between the vanes and the eccentric ring as the vanes slide in the ring. The wear is caused by drag between the vane tips and inner surface of the ring. This can cause a significant amount of torque loss. Another problem can be contamination within the pump which can affect reliability.

Accordingly, there exists a need for an improved sliding vane pump which has improved efficiency, improved packaging, and has a reduction of wear between the vanes and the outer rotor.

SUMMARY OF THE INVENTION

The present invention includes a variable displacement pump having an inner rotor rotatable about a first axis having at least two slots, with the slots substantially extending diametrically through the width of the inner rotor. The present invention also includes at least two vanes, each located in a distinct one of said at least two slots. The pump also has an outer rotor rotatable about a second axis and operably associated with the inner rotor. The outer rotor has two or more recesses, each configured to receive one of said at least two vanes. The pump also includes an expandable chamber formed by the outer rotor and the inner rotor, and an eccentric ring surrounding the outer rotor. Also included is a housing having an eccentric ring located within the housing for adjusting the relative relationship between the first axis and the second axis in order to vary the displacement of the pump.

Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

FIG. 1 is a sectional side view of a sliding vane pump with the outer rotor aligned with the inner rotor, according to the present invention;

FIG. 2 is a sectional side view of a sliding vane pump with the outer rotor offset from the inner rotor;

FIG. 3 is an exploded view of a sliding vane pump, according to the present invention;

FIG. 4 a perspective view of a vane used in a sliding vane pump, according to the present invention;

FIG. 5 is a side view of a vane used in a sliding vane pump, according to the present invention;

FIG. 6 is a perspective view of a hub and inner rotor used in a sliding vane pump according to the present invention;

FIG. 7 is a perspective view of an alternate embodiment of a sliding vane pump with the cover and housing removed, according to the present invention;

FIG. 8 is a perspective view of a rotor used in an alternate embodiment of a sliding vane pump, according to the present invention;

FIG. 9 is an first exploded view of an alternate embodiment of a sliding vane pump, according to the present invention; and

FIG. 10 is a second exploded view of an alternate embodiment of a sliding vane pump, according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

Referring to the Figures generally, a sliding vane pump according to the present invention is generally shown at 10. The pump 10 has an inner rotor 12 which rotates about a first axis 14. The inner rotor 12 also has a series of slots 16 for receiving a plurality of vanes 18. The vanes 18 have a first side 20 which is offset and parallel to a second side 22. The vanes 18 also have a third side 21 which is parallel to and equal in length compared to a fourth side 23. Both the third side 21 and fourth side 23 serve as a flat engagement 24. The vane 18 also includes an extension 26 which is of a reduced width compared to the remainder of the vane 18. The pump 10 also has an outer rotor 28 which rotates about a second axis 30, and has recesses 32 for receiving the flat engagements 24 of the vanes 18.

The first side 20 being offset from the second side 22 creates an angle 27 between the flat engagements 24 and the first side 20, as well as between the flat engagements 24 and the second side 22. The recesses 32 are in sliding contact with each of the flat engagements 24. An individual example of one of the vanes 18 is depicted in FIGS. 4 and 5.

Surrounding the outer rotor 28 is an eccentric ring 34 located within a housing 36. Located in between the inner rotor 12 and the outer rotor 28 is an expandable chamber 38 used for pumping fluid. The housing 36 also includes an inlet port 40 for delivering fluid into the expandable chamber 38, and an outlet port 42 for receiving fluid from the expandable chamber 38. There is also an inlet aperture 43 in fluid communication with the inlet port 40, where fluid is fed into the inlet port 40 via the inlet aperture 43 prior to being pumped by the pump 10. There is also an outlet aperture 45 in fluid communication with the outlet port 42; once the fluid is pumped by the pump 10, the fluid passes from the outlet port 42 through the outlet aperture 45 to a device requiring pressurized fluid.

The eccentric ring 34 includes a flange 44, a pivot hole 46, and a pivot pin 47 received in the pivot hole 46. The pivot hole 46 and pivot pin 47 connect the eccentric ring 34 to the housing 36, so as to allow the eccentric ring 34 to pivot about the pivot pin 47. The flange 44 is also connected to a bias mechanism such as a spring on one side, and a piston on the opposite side, such that force can be applied to the flange 44, changing the eccentricity between the inner rotor 12 and the outer rotor 28, the function of which will more clearly be described later.

In operation, the inner rotor 12 is affixed to, and driven by a hub 48. The inner rotor 12 turns and applies force to and drives the vanes 18. The flat engagement 24 of the first end 20 and the second end 22 then applies force to the recesses 32 of the outer rotor 28. Because the recesses 32 are located at an angle which is identical to the angle 27 of the vanes 18, the recesses 32 are in flush contact with the flat engagements 24, allowing the flat engagements 24 to apply force to the recesses 32, and drive the outer rotor 28. The outer rotor 28 is allowed to rotate relative to the eccentric ring 34 because of a hydrodynamic journal bearing 50 located therebetween. The hydrodynamic journal bearing 50 in this embodiment is a hydrodynamic film which minimizes friction between the outer rotor 28 and the eccentric ring 34. However, the hydrodynamic journal bearing 50 could also be a ball bearing, a type of grease, or any other device which would reduce friction between the outer rotor 28 and the eccentric ring 34.

The pump 10 has the ability to vary the amount of fluid pumped from the inlet port 40 to the outlet port 42. When the pump 10 is in the position shown in FIG. 1, the first axis 14 of the inner rotor 12 and the second axis 30 of the outer rotor 28 are aligned. When the first axis 14 is aligned with the second axis 30, no fluid is transferred from the inlet port 40 to the outlet port 42. As force is applied to the flange 44, the eccentric ring 34 will pivot about the pivot pin 47 located in the pivot hole 46. As the eccentric ring 34 pivots, the outer rotor 28 will move as well. The outer rotor 28 can be moved to a maximum position shown in FIG. 2. In this position, fluid will be drawn into the expandable chamber 38 and inbetween each of the vanes 18 from the inlet port 40 because the position of the outer rotor 28 and the expandable chamber 38 creates a suction as the inner rotor 12 and outer rotor 29 rotate, and the vanes 18 move across the inlet port 40.

As the inner rotor 12, the outer rotor 14, and the vanes 18 continue to rotate, the amount of fluid in the expandable chamber 38 will reach a maximum volume, and then the expandable chamber 38 will begin to compress the fluid. The expandable chamber 38 will compress the fluid between the vanes 18 even further as the inner rotor 12 and outer rotor 28 rotate, and the vanes 18 move across the outlet port 42. The contraction of the fluid between each of the vanes 18 will force the fluid through the outlet port 42. To compensate for the change in eccentricity between the outer rotor 28 and the inner rotor 12, the flat engagement 24 of the vanes 18 are allowed to slide in the recesses 32, while still transferring rotational force to the outer rotor 28.

Another aspect of the invention which provides advantages over previous vane pumps is that the vanes 18 are in a “stacked” configuration, which is best seen in FIG. 3. As previously mentioned, each vane 18 has an extension 26 formed as a portion of each vane 18. The width of each extension 26 is narrower than the overall width of the vane 18. Each extension 26 is also located in a different location along the width of the vane 18. This allows the vanes 18 to “stack” together, allowing all the vanes 18 to be inserted into a corresponding slot 16 in the inner rotor 12. In this particular embodiment, there are four vanes 18: a first vane 52, a second vane 54, a third vane 56, and a fourth vane 58.

As can be seen in FIG. 3, the extension 26 of the first vane 52 is adjacent to the extension 26 of the second vane 54, the extension 26 of the second vane 54 is adjacent to the extension 26 of the third vane 56, and the extension 26 of the third vane 56 is adjacent to the extension 26 of the fourth vane 58. Each extension 26 is adjacent to one another, but will be at a different angle relative to one another because of each vane 18 being located in a corresponding slot 16 in the inner rotor 12.

The present invention is not limited to having four vanes 18, as described above. The number of vanes 18 can be changed to suit any particular application requiring a sliding vane pump 10 of the present invention. In this embodiment, since there are four vanes 18, the width of each extension 26 is approximately 25% of the total width of each vane 18. If more or less vanes 18 were used, the width of the extension 26 would change proportionately. For example, if six vanes were used, each extension would be ⅙ of the total width of the vane 18; if two vanes 18 were used, the width of each extension 26 would be half of the total width of the vane 18.

The present invention has several advantages over other types of sliding vane pumps and articulated vane pumps. The sliding vane pump 10 of the present invention has a lower number of vanes 18, but still performs as effectively, and has higher volumetric efficiency. Also, the vanes 18 having the flat engagements 24 driving the outer rotor 28 in the manner described by the present invention reduces the amount of wear on the flat engagements 24 and the outer rotor 28, the amount of contact stress on the vanes 18 is also reduced when compared to a conventional sliding vane pump. The engagement between the flat engagements 24 of the vanes 18 and the recesses 32 also provides for the ability to prime the pump 10 at start up. This eliminates additional components such as guide rings and/or oil pressure, which are used to prime typical sliding vanes pumps. The pump 10 of the present invention is also facilitates easier assembly during manufacturing, and is more packaging efficient. The integrated structure of the vanes 18 also eliminates or reduces the centrifugal effect. Noise, vibration, and harshness (NVH) is improved because the vanes 18 are more dynamically balanced, and there is an increased resistance to contamination which can inhibit performance.

An alternate embodiment of the present invention is shown in FIGS. 7-10, wherein like numbers refer to like elements. The pump 10 shown in FIGS. 7-10 includes a straddle support inner rotor, generally shown at 60. The inner rotor 60 also includes a series of slots 62. However, the slots 62 of this embodiment differ from the first embodiment in that two of the slots 62 are elongated slots 64, and two of the slots 62 are not elongated slots 66. The inner rotor 60 also includes two hub portions 68, and a series of vane supports 70, which are used to support a series of vanes.

In this embodiment, two of the vanes are multi-piece vanes 76, and two of the vanes are single piece vanes 78. The single piece vanes 78 are similar to the first vane 52 and fourth vane 58, respectively, of the first embodiment. The multi-piece vanes 76 are similar to the second vane 54 and third vane 56, respectively, with the exception that the multi-piece vanes 76 are divided into two parts. The extensions 26 are divided in half.

During assembly, the multi-piece vanes 76 are inserted into the non-elongated slots 66, and the single piece vanes 78 are inserted into the elongated slots 64. The function of the elongated slots 64 is to allow the single piece vanes 78 to be inserted through the inner rotor 60. More specifically, the elongated slots 64 allow the widest part of the vane 78 to be inserted through the rotor 60 without being blocked by or receiving any interference from the extensions 26 of any of the other vanes. Once the multi-piece vanes 76 and the single piece vanes 78 are inserted into the slots 62, the rotor 60 is inserted into the outer rotor 28 in a similar manner as in the previous embodiment. The vanes will also engage the recesses 32 of the outer rotor 28 in a similar manner to the first embodiment.

Once all of the vanes are inserted into the slots 62, the housing 36 will prevent the vanes from sliding out of the slots 62 because the inside surface of the housing 36 will be in sliding contact with each of the vanes.

The inner rotor 60 is supported on both sides of the vane supports 70 by the hub portions 68; this provides additional structural support and allows for an increased pressure capacity of the pump 10. The inner rotor 60 is driven by the shaft; the rotor 60 turns and applies force to the vanes, and the vanes in turn apply force to the recesses 32, driving the outer rotor 60 in a similar manner compared to the previous embodiment.

To vary the amount of fluid that is pumped in this embodiment of the present invention, the flange 44 is inserted into a recess 80 of a piston 82. The piston 82 includes a hollow portion 84 which receives a portion of a return spring 86. On the opposite side of the piston 82 is a flat portion 88 which receives pressure from fluid. When the fluid pressure on the flat portion 88 of the piston 82 is greater than the pressure applied to the piston 82 from the return spring 86, the piston 82 will move to the right when looking at FIG. 7, and the eccentric ring 34 will pivot in the same manner as the previous embodiment, and the amount of fluid pumped will decrease. When the fluid pressure on the piston 82 is relieved, the force applied to the piston 82 from the return spring 86 will cause the eccentric ring 34 to return to its original position to increase the displacement, as shown in FIG. 7, which is the default position for the eccentric ring 34, where the first axis 14 is aligned with the second axis 30.

The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention. 

1. A variable displacement pump, comprising: an inner rotor rotatable about a first axis having at least two slots, said at least two slots substantially extending diametrically through the width of said inner rotor; at least two vanes, each located in a distinct one of said at least two slots; an outer rotor rotatable about a second axis and operably associated with said inner rotor, said outer rotor having two or more recesses, each configured to received one of said at least two vanes; an expandable chamber formed by said outer rotor and said inner rotor; an eccentric ring surrounding said outer rotor; and a housing having said eccentric ring located within said housing for adjusting the relative relationship between said first axis and said second axis in order to vary the displacement of said pump.
 2. The variable displacement pump of claim 1, further comprising: a flange formed as part of said eccentric ring; a pivot hole formed as part of said eccentric ring; and a pivot pin formed as part of said housing such that said pivot pin is disposed within said pivot hole of said eccentric ring such that a force is applied to said flange, thereby causing said eccentric ring to pivot about said pivot pin and the position of said first axis to become aligned with or offset from said second axis.
 3. The variable displacement pump of claim 1, further comprising: an inlet port formed as a portion of said housing; and an outlet port formed as a portion of said housing such that when said inner rotor rotates, said at least two vanes will apply force to said at least two recesses of said outer rotor, causing said outer rotor to rotate, and when said first axis is offset from said second axis, said at least two vanes and said expandable chamber will transfer fluid from said inlet port to said outlet port.
 4. The variable displacement pump of claim 1, wherein each of said at least two vanes is further comprised of: a first side offset and parallel to a second side; a third side connected to said first side and said second side; a fourth side connected to said first side and said second side, with either of said third side or said fourth side forming at least one flat engagement; and an extension of a reduced width in relation to the width of said third side and said fourth side, and said flat engagement is positioned at an angle relative to said first side and said second side, and is engaged with one of said at least two recesses of said outer rotor.
 5. The variable displacement pump of claim 4, wherein said flat engagement of each of said at least two vanes is slidably engaged with one of said at least two recesses of said outer rotor.
 6. The variable displacement pump of claim 5, wherein each of said at least two recesses is positioned at an angle which corresponds to said angle of said flat engagement, allowing said at least two vanes to transfer rotational force to said outer rotor.
 7. The variable displacement pump of claim 6, wherein said extension of one of said at least two vanes is adjacent to said extension of another of said at least two vanes, placing said at least two vanes in a stacked configuration.
 8. The variable displacement pump of claim 1, wherein said inner rotor is a straddle support inner rotor, comprising: a first hub portion; a series of vane supports connected to said first hub portion; a second hub portion connected to said series of vane supports on the opposite side of said vane supports in relation to said first hub portion; and said at least two slots further comprising at least two elongated slots, each of said at least two elongated slots extending into a portion of either said first hub portion or said second hub portion.
 9. The variable displacement pump of claim 8, one of said at least two vanes further comprising a multi-piece vane which is received into one of said at least two slots.
 10. The variable displacement pump of claim 1, further comprising; a piston; a flange formed as a portion of said eccentric ring; a recess formed as a portion of said piston, said flange of said eccentric ring partially disposed in said recess; a substantially flat portion formed as a portion of said piston; a hollow portion formed as a portion of said piston; and a return spring at least partially disposed in said hollow portion of said piston such that said return spring biases said first axis to be aligned with said second axis, and fluid pressure is applied to said substantially flat portion to overcome the force of said return spring such that said piston moves cause said flange to pivot said eccentric ring, thereby causing said first axis to become offset from said second axis.
 11. The variable displacement pump of claim 1, wherein said at least two vanes will remain substantially stationary relative to said at least two recesses, when said first axis is substantially aligned with said second axis.
 12. A sliding vane pump, comprising: a housing; an inner rotor having a series of slots, said inner rotor operably positioned in said housing and rotatable about a first axis; said housing having an inlet port and an outlet port; a series of vanes, each of said series of vanes having a first side offset and parallel to a second side, a third side connected to said first side and said second side to form a flat engagement, and a fourth side connected to said first side and said second side to form a flat engagement, and an extension of a reduced width in relation to said the width of said third side and said fourth side, said series of vanes received by said series of slots; an outer rotor having a series of recesses, each for receiving one of said series of vanes; an expandable chamber located between said inner rotor and said outer rotor; and an eccentric ring which circumscribes said outer rotor and is located within said housing, said eccentric ring having a flange, and a pivot hole, and when said inner rotor rotates, said series of vanes will rotate and drive said recesses of said outer rotor, causing said outer rotor to rotate, and when said first axis is offset from said second axis, said expandable chamber will transfer fluid from said inlet port to said outlet port, and when said first axis is aligned with said second axis, said expandable chamber will not transfer fluid from said inlet port to said outlet port.
 13. The sliding vane pump of claim 12, said housing further comprising a pivot pin formed as a portion of said housing, wherein said pivot pin is inserted through said pivot hole such that a force is applied to said flange, thereby causing said eccentric ring to pivot about said pivot pin, changing the position of said first axis in relation to said second axis.
 14. The sliding vane pump of claim 12, further comprising: an angle between said flat engagement of said third side in relation to said first side and said second side; and an angle between said flat engagement of said fourth side in relation to said first side and said second side.
 15. The sliding vane pump of claim 14, wherein said series of recesses are positioned at said angle to slidably engage said flat engagement of said first end and said flat engagement of said second end.
 16. The sliding vane pump of claim 12, wherein said inner rotor is a straddle support inner rotor, further comprising: a series of vane supports, said series of slots formed by said series of vane supports; a first hub portion connected to said series of vane supports; and a second hub portion connected to said series of vane supports on the opposite side of said series of vane supports in relationship to said first hub portion.
 17. The sliding vane pump of claim 16, said series of slots further comprising: at least two elongated slots formed by said series of vane supports, wherein two of said series of vanes are disposed within said at least two elongated slots.
 18. The sliding vane pump of claim 16, said series of vanes further comprising at least two multi-piece vanes, wherein said at least two multi-piece vanes are disposed within two of said at least two slots.
 19. The sliding vane pump of claim 12, further comprising: a piston having a recess formed as a portion of said piston, said recess receives a portion of flange of said eccentric ring; a substantially flat portion formed as a portion of said piston; and a hollow portion formed as a portion of said piston, said hollow portion operable for receiving a portion of a return spring such that said return spring biases said first axis of said inner rotor to be aligned with said second axis of said outer rotor, and said piston applies a force to said flange to cause said eccentric ring to pivot about said pivot hole and said first axis to become offset from said second axis when fluid pressure is applied to said substantially flat portion.
 20. The sliding vane pump of claim 12, further comprising said flat engagement of said first end of said series of vanes and said flat engagement of said second end of said series of vanes will slide in said recesses when said series of vanes rotate said outer rotor, and said first axis is offset from said second axis.
 21. The sliding vane pump of claim 12, further comprising said flat engagement of said first end of said series of vanes and said flat engagement of said second end of said series of vanes will remain substantially stationary relative to said recesses when said series of vanes rotate said outer rotor, and said first axis is substantially aligned with said second axis.
 22. A sliding vane pump which is used for pumping fluid, comprising: an inner rotor rotatable about a first axis, said inner rotor having a series of slots; a first vane received into one of said series of slots; a second vane received into another of said series of slots; a third vane received into another of said series of slots; a fourth vane received into another of said series of slots; each of said first vane, said second vane, said third vane, and said fourth vane having a first side, a second side, an extension, a third side having a flat engagement, and a fourth side having a flat engagement; an outer rotor having a series of recesses, each of said series of recesses for receiving one of said flat engagement of said third side or said flat engagement of said fourth side, said outer rotor rotatable about a second axis; an expandable chamber formed between said inner rotor and said outer rotor; a housing having an inlet port and an outlet port; and an eccentric ring which circumscribes said outer rotor and is located within said housing, said eccentric ring having a flange and a pivot hole, and said inner rotor rotates about said first axis, driving said first vane, said second vane, said third vane, and said fourth vane, and said outer rotor rotates about said second axis, causing said first vane, said second vane, said third vane, and said fourth vane to drive said series of recesses of said outer rotor, thereby rotating said outer rotor.
 23. The sliding vane pump which is used for pumping fluid of claim 22, further comprising a pivot pin formed as a portion of said housing, said pivot pin being disposed within said pivot hole such that said flange of said eccentric ring receives a force to cause said eccentric ring to pivot about said pivot pin, and the position of said inner rotor to change in relation to outer rotor.
 24. The sliding vane pump which is used for pumping fluid of claim 22, further comprising said first axis to be substantially aligned with said second axis to cause said first vane, said second vane, said third vane, and said fourth vane to remain stationary relative to said series of recesses.
 25. The sliding vane pump which is used for pumping fluid of claim 22, further comprising said first axis to be offset from said second axis to cause said expandable chamber, said first vane, said second vane, said third vane, and said fourth vane to transfer fluid from said inlet port to said outlet port.
 26. The sliding vane pump which is used for pumping fluid of claim 22, further comprising said first side of each of said first vane, said second vane, said third vane, and said fourth vane to be offset and parallel to said second side of each of said first vane, said second vane, said third vane, and said fourth vane.
 27. The sliding vane pump which is used for pumping fluid of claim 25, further comprising an angle between said flat engagement of said third side in relation to said first side and said second side, and said angle is also between said flat engagement of said fourth side in relation to said first side and said second side.
 28. The sliding vane pump which is used for pumping fluid of claim 26, further comprising said series of recesses to be positioned at said angle of said flat engagement of said third side and said flat engagement of said fourth side.
 29. The sliding vane pump which is used for pumping fluid of claim 22, further comprising said first vane, said second vane, said third vane, and said fourth vane are stacked such that said extension of said first vane is adjacent to said extension of said second vane, said extension of said second vane is adjacent to said extension of said first vane and said extension of said third vane, said extension of said third vane is adjacent to said extension of said second vane and said extension of said fourth vane, and said extension of said fourth vane is adjacent to said extension of said third vane.
 30. The sliding vane pump which is used for pumping fluid of claim 22, wherein said inner rotor is a straddle support inner rotor, comprising: a first hub portion; a plurality of vane supports, said first hub portion being connected to said plurality of vane supports; a second hub portion, said second hub portion being connected to said plurality of vane supports on the opposite side of said plurality of vane supports in relation to said first hub portion; and two of said series of slots further comprise at least two elongated slots, wherein said first vane is inserted through one of said at least two elongated slots, and said fourth vane is inserted through another of said at least two elongated slots.
 31. The sliding vane pump which is used for pumping fluid of claim 22, each of said second vane and said third vane further comprising: a multi-piece vane divided along said extension, wherein said multi-piece vane is inserted into one of said series of slots.
 32. The sliding vane pump which is used for pumping fluid of claim 22, further comprising: a piston having a substantially flat portion and a hollow portion; a recess formed as a portion of said piston, said recess receiving a portion of said flange of said eccentric ring; and a return spring partially disposed in said hollow portion, and in contact with a portion of said housing such that said return spring biases said piston to locate said flange of said eccentric ring and said eccentric ring position said first axis substantially in alignment with said second axis, and said first axis will become offset from said second axis when a force is applied to said flat portion of said piston that is greater than the force applied to said piston by said return spring. 